1. Field of Invention
This invention generally relates to airplane navigation, specifically to a handheld mechanical computer which works in tandem with an onboard GPS unit for navigating to, entering, and flying the traffic pattern of any uncontrolled airport.
2. Prior Art
The Global Positioning System has provided a revolution in aircraft navigation giving pilots the ability to precisely navigate direct to any airport using an onboard GPS receiver. Unfortunately, pilots need additional navigational guidance beyond direct to the airport during a visual approach to an uncontrolled airport. Pilots approaching an uncontrolled airport are encouraged to make a “preferred traffic pattern entry” in order to provide for an orderly traffic flow in the traffic pattern and minimize the chances of a collision. In addition to aircraft approaching and departing an airport, frequently there are aircraft making multiple loops in the traffic pattern practicing takeoffs and landings. An illustration of the traffic pattern and the preferred traffic pattern entry is shown in FIG. 7. The traffic pattern is comprised of five legs; the departure leg 126, the crosswind leg 127, the downwind leg 122, the base leg 123, and the final approach leg 124. FIG. 7 illustrates a left traffic pattern as turns are made to the left in the pattern. Although the majority of runways have left traffic, some runways have right traffic. FIG. 8 illustrates a right traffic pattern as turns are made to the right in the pattern. Note that the right traffic pattern is a mirror image of the left traffic pattern.
The preferred traffic pattern entry requires that pilots enter the downwind leg of the traffic pattern at midfield approximately ½ to ¾ miles from the runway at a 45 degree angle. The pilot should be established on the 45 degree intercept course several miles from the airport. Although the minimum actual distance from the airport that the pilot should be established on the 45 degree intercept course is left to the pilot's discretion, three miles is believed to be a good rule of thumb. From the above description of the preferred traffic pattern entry, it is shown that there is an approach point that a pilot must navigate to in order to make a proper traffic pattern entry. The preferred traffic pattern entry or “45 entry” is illustrated by the course line 121 on FIG. 7.
Writings on entering and flying the traffic pattern do not actually refer to an approach point that should be flown to prior to making the preferred traffic pattern entry. Nonetheless, the definition of the preferred traffic pattern entry requires pilots to navigate to a relatively small area or point prior to making the preferred traffic pattern entry. This point will subsequently be referred to as the “pattern approach point”.
Pilots can easily navigate direct to airports using GPS as GPS units are programmed with the location or coordinates of all public use airports. The pilot simply enters the identifier for the airport and the GPS provides the pilot a desired course or track to the airport from the current location, cross track or deviation from the desired track, distance to the airport and current bearing to the airport. Pattern approach points are not preprogrammed in GPS units and although the approach points could be manually entered, it is not practical to do so. The location of the approach point would need to be calculated and than manually entered into the GPS.
Without a practical navigation aid, pilots are left to their own intuition and estimation on what course to fly in order to navigate to the pattern approach point. This imprecise navigation technique can result in one of several scenarios that could increase the chances of a collision with another aircraft in the congested airspace frequently encountered around airports. One scenario is that the pilot flies through the traffic pattern at an undesirable course while enroute to the traffic pattern entry approach point. Another scenario is that the pilot approaches the downwind leg at an intercept course substantially different than 45 degrees which reduces the pilot's ability to spot aircraft in the traffic pattern and or make a smooth pattern entry. Still another scenario is that an unseasoned pilot gets so overwhelmed with navigating to the pattern approach point that position announcements on the advisory frequency and or proper traffic scanning are neglected.
Some pilots navigate to the preferred traffic pattern entry approach point by first flying over the airport at least 500 feet above the traffic pattern altitude and then flying away from the airport on a course that will allow them to make a turn back towards the airport and make a proper preferred traffic pattern entry. This modified version of the preferred traffic pattern entry is called the “preferred entry-crossing midfield” (FIG. 9). While this is the preferred method of entering the traffic pattern for aircraft approaching the airport from the opposite side of the runway on a course that would result in the aircraft flying near the traffic pattern while navigating to the pattern approach point, for the majority of courses to the airport this method needlessly increases flying time and increases the chance of a collision with another aircraft as the pilot descends to pattern altitude and turns back toward the airport to make the preferred traffic pattern entry.
In addition to the two versions of the preferred traffic pattern entry, there are two commonly used alternate traffic pattern entries used by pilots which are deemed acceptable under certain circumstances. The first alternate traffic pattern entry is called the “alternate midfield entry” (FIG. 10) which can be used in lieu of the preferred entry-crossing midfield. This pattern entry eliminates the excessive maneuvering in the congested airspace around airports required by the preferred entry-crossing midfield. The alternate midfield entry requires that the pilot cross the runway halfway between midfield and the departure end of the runway at pattern altitude and turn directly into the downwind leg. The second alternate traffic pattern entry is the “straight-in approach” (FIG. 11). This approach eliminates flying all legs of the pattern other than the final leg. The pilot should be established on final several miles from the airport.
The introduction of the alternate traffic pattern entries reveals another dilemma for the pilot approaching an uncontrolled airport. Which traffic pattern entry should be used? In addition to the aircraft's course to the airport, other factors going into this decision are the pilots personal preferences and experience level, volume of traffic expected at the airport, weather, nearby restricted airspace and obstructions.
Regardless of which of the four commonly used traffic pattern entries is selected, in order to make a proper traffic pattern entry, the pilot must navigate to a pattern approach point while remaining well clear of the traffic pattern until the traffic pattern is actually entered.
There are no known devices that will effectively assist pilots in selecting a traffic pattern entry or in navigating to a pattern approach point. There are traffic pattern computers marketed, but they only tell the pilot entry and pattern headings for the various legs of the traffic pattern. They do not provide pilots navigational guidance to the pattern approach point. Also, these devices only marginally assist pilots in selecting a traffic pattern entry. First, these devices do a very poor job helping the pilot to visualize the aircraft's position in relationship to the traffic pattern as the aircraft approaches the airport. The diagrams on these devises do not show to scale the aircrafts position in relationship to the traffic pattern when the aircraft is at distance from the airport that a pilot would normally break off direct to airport navigation and fly to a pattern approach point. Second, these devices do not provide any explicit guidance rather a given pattern approach point can be directly navigated to from the aircraft's current position without flying too close to the traffic pattern before actually entering the traffic pattern. The best example of these devices is U.S. Pat. No. 3,100,601 to Shapiro (1963). Other similar devices are U.S. Pat. No. 4,274,204 to Self (1981), and U.S. Pat. No. 2,996,242 to Bannister (1961).